The car was stopped between junction 33 and 34 on the southbound carriageway of the M1.

Police said they had recovered two non-automatic guns and a small amount of ammunition.

It is not clear whether the terror plot was imminent but with the anniversary of the July 7 bombings due this weekend and the Olympics about to begin, it is feared the attack had gone beyond the planning stage.

Detective Chief Superintendent Kenny Bell, head of the West Midlands Counter Terrorism Unit, said: "As soon as the items were discovered in the impounded vehicle, our priority was to protect the public by pursuing and arresting those we believed to be involved."

It follows the arrest of five men and a women in an intelligence-led anti-terrorism operation in nine addresses across London yesterday.